This invention relates to a continuously variable transmission which can be used in an automotive or other application.
A traction fluid allows a friction drive to be transferred between two steel interfaces e.g. in a pulley and belt transmission or in a toroidal transmission. However torque transmission capability and mechanical efficiency are adversely affected by the following:    (1) in a pulley and belt transmission, power is transmitted from a first pulley via a friction drive to a belt and then from the belt through another friction drive to a second pulley. In a toroidal transmission, power is transmitted from a first toroid to a roller and then from the roller to a second toroid. Thus, in each case, there are two friction interfaces in series, a configuration which compounds mechanical losses. For example if the efficiency of each interface is 90% then the efficiency of two interfaces in series is 81%;    (2) an input friction radius, and an output friction radius, of a friction interface vary as a drive ratio varies. For a given input torque, as the drive ratio changes, this variation requires a variable clamping force which is typically effected by means of a hydraulic control system which includes a hydraulic pump the use of which decreases mechanical efficiency;    (3) the variation in the input radius, and in the output radius, limit the torque output, particularly when the input friction radius is at a minimum. This means that the transmission cannot handle a maximum value of input torque through its ratio range, and use must be made of a torque-limiting mechanism which, typically, is electronically controlled to limit engine power and torque in the relevant ratios; and    (4) when an output speed is slightly above zero more torque may be called for than what the friction drive can supply. If the friction drive forms a part of a transmission which is installed in a vehicle it may not be possible for the vehicle to move from a rest position over a kerb or a similar small obstacle.
GB (1913) 14696 describes a frictional transmission which includes a driver wheel peripherally engaged with planar surfaces of opposed disks. The arrangement is one in which substantial forces are generated, due to an asymmetrical distribution.
GB(1912) 29132 describes a frictional drive arrangement in which a drive mechanism engages peripherally with two wheels and imparts counter-rotating drive to two disks. An adjustable output drive is provided by wheels which are axially movable along shafts which are rotated by the disks. The construction is not compact for a substantial volume exists between the disks. Also, the drive mechanism is loaded by the disks in one direction and requires components of a substantial strength to cater for these unidirectional loads.
An object of the present invention is to provide a continuously variable transmission (CVT) with a radial drive, of compact form, which has a balanced construction which helps to resist loading effects.